Current-limiting device



B. E. GETCHELL.

CURRENT LIMITING DEVICE.

APPLICATION FILED AUG. 25, I917.

Patented Aug. 29, 1922.

4 SHEETS-SHEET I.

B. E. GETCHIELLI CURRENT LIMITING DEVICE.

'APPLICATION FILED Aue.25, 1912.

1,427,203] v Patented Aug. 29, 1922.

B. E- GETCHELL.

CURRENT LIMITING DEVICE.

APPLICATION FILED Aue,25, 1917.

Patented Aug. 29, 1922.

4 SHEETS-SHEET 3.

V MKAMMMMM vvvvvvvvvv B. E. GETCHEL'L.

CURRENT LlMiTING DEVICE.

APPLICATION FILED AUG-25, 1917- 1,427,203 Patented Aug. 29, 1922.

4 SHEETS-SHEET 1.

UNI-TED s'rAras PATENT OFFICE.

BENJAMIN a. GETCHELL, or GBEENSBURG, PENNSYLVANIA, ABSIGNOR T0 RAILWAY AND INDUSTRIAL ENGINEERING COMPANY, or GREENSBURG, rnNNsnvaNrafa CORPORATION OF PENNSYLVANIA.

' CURRENT-LIMITING mivicm Specification of Letters I'atent. Pafented Aug. 29, 1922 Application filed August 25, 1917'. Serial No. 188,258.

To allwhom it may concern:

Be it known that I, BENJAMIN E; GETCH- ELL a citizen of the United States, residing at Greensburg, in the county of Westmoi'eland and State of Pennsylvania, have invented certain new and useful Improvements in Current-Limiting Devices, of which the following is a specification.

This invention relates to controlling devices for electric circuits, and more particularly to devices for limiting the amount of current supplied to' consumers in systems where meters are not employed.

In such systems it is the common practice to serve customers on what is known as a flat rate basis, the contract permitting the consumer to use any amount of current he desires up to a certain maximum, in consideration of fixed monthly or yearly payments. Obviously, it is necessary to prortect the service company by providing means for preventing a consumer from using more current than his contract calls for.

Various devices have heretofore been proposed for accomplishing this purpose, many of thembeing electromagnetically operated and usually serving to-cause a rapid flickering of the lights in case an attempt is made to use too much current. These prior devices have been found more or less defective in practice, owing to rapid deterioration of the contacts, or to other causes. With some of them it has been found possible to operate heating apparatus even though consuming an excessive amount of'current, since the making and breaking of the current occurs with such rapidity as to maintain such apparatus at least in partially operative condition.

The object of the present invention is therefore to provide an improved device of this character in which the interruptions of the circuit take place much more slowly, and in which the ratio between the on and oil periods can be adjusted as desired. It is obvious that by making the oil eriod relatively large, it will be impossi le to maintain the temperature of heating apparatus when the predetermined load is exceeded. A further object is to provide a device in which the circuit is made but never broken at the controlling contacts, thereby preventing deterioration of such contacts due to sparking. To this end, the invention contemplates the use of a hot wire or thermal element for closing the controlling circuits, such circuits containing electromagnetic means for opening and closing the main circuit.

The principles involved in the invention admit of application to many varying conalternating circuit, where it is desired to dim the lights instead of extinguishing them;

. Fig. 3 is a view similar to Fig. 1, but showing a slightly different method of connecting the electromagnetic controlling means; I

Fig. 4 is a view similar to Fig. 3, except that the device is arranged for dimming the lights instead of extinguishing them;

Fig. 5 is a view similar to Fig. 4, showing another method of dimming;

Fig. 6 is similar to Fig. 1, except that it is applicable only to alternating current circuits, a transformer being employed;

Fig. 7 shows a similar arrangement, except that the controlling current is obtained from a secondar winding on the electromagnetic means itself instead of a separate transformer;

Fig. 8 is a view showing the application of my improved controlling device to a threewige circuit employing alternating currents; an

Fig. 9 is a view similar to Fig. 8 but showing the controlling device applied to a twophase alternating current circuit.

Referring to the drawings in detail, and particularly to Fig. 1, the incoming line wires are designated by land 2. These are connected to the binding posts 3-4 of the controlling device, while other binding posts I 56 thereof receive. the mains 8-9, to which the load 10 is connected. The wires 2 and 9 are, in fact, continuous, since the binding posts 4 and 5 are joined by a cross connection 7. v

The essential part of my improved controling In the conductor" 28 is interposed a ans sists of a spring 'ries with the load, the current passin lin device is a thermal element or hot wire 15, eld at its ends in fixed binding posts 13 and 14. ,This' hot wire is connected at. its middle 16, by means of a conducting link 17, with a resilient contact finger or switch member 18. This contact finger preferably contrip having at one'end a spiral 19, secure at its center to a fixed support 19'. The free end of the spring 18 plays between adjustable contact points 20 an 21, as will. be hereinafter more fully described. I'n addition'to the thermal element 15, I provide an electromagnetic switch actuating device which is here re resented as comprising a pair ofsolenoi coils 23 and 26, in which works a common core 32.

The thermal element 15 is connected in se- 111 from binding post 3, over wire 28, to bindpost 13, thence through the wire 15 to bindlng post 14, whence 1t passes through conductor 8, binding post 6, wire 8, to loadi air 0 spaced contacts 29, adapted to be bri ged by a switchmember 30, carried by a rod 31, secured to the core 32 of the solenoid.

The contact 20 is connected by a wire 22 with one end of the coil 23, the other end of which is connected by wire 24 to one side of the line: at binding post 5. The contact 21 is connected b wire 25 with one end of the coil 26, the ot or end of which is connected by wire 27 to the other side of the line at binding'post 3. I

The 0 eration of the device shown in Fig. 1 is as ollows: Upon the occurrence of an overload on the mains 8-9, the wire 15 is excessively heated and caused to expand. This permits the contact finger 18 to move .underthe influence of the spring 19 until it engages contact 20. Thereupon a circuit is closed through the solenoid 23 as follows: From linel, through wire 28, hot wire 15, conducting link 17,.contact finger 18, contact 20, wlre 22, solenoid 23, wire 24 to the other side 2 of the line. This energizes solenoid 23 which draws the core 32 to the right, thus breaking the main circuit at switch contacts 29. It will be noted that the opening of these contacts also interrupts the circult just traced through solenoid 23 so that this solenoid cuts itself out when it operates.

Immediately after the circuit is opened the wire 15 begins to cool and contract, drawing the contact finger 18 over towards con-.

tact 21. After a definite time interval, such contraction causes 18 to engage 21 and there i tact finger 18, conducting line 17 hot wire 15, binding post ,14, conductors 8' and 8, through the load 10 to conductor 9, and thence back to the other side of theline.

This energizes solenoid 26 and causes the core 32 and switch 30 to be restored to the position shown in the drawings, thus again closing the main line circuit. It will be seen therefore that the solenoids 23 and 26 are energized only momentarily and that the operation of each serves to deprive itself of current. It will also be observed that the circuit is onlymade at the contacts mined. By adjusting the contact point 21 the duration of the period of cut-off is determined. This period may, of course, be lengthened by covering the hot wire 15 with a protective coating of asbestos or the like, which tends to retard heat radiation.

It will be obvious that the greater the overload the shorter will be the period during which the circuit remains closed, since a shorter time will be required to heat the thermal element. The time that the circuit. remains open, however, is substantially always the same and is overned by the predetermined setting of t e contact.

This thermally controlled interruptor or current limiting device will, it is seen, operate at a comparatively low rate of speed. That is to say, instead of rapid vibrations of 200 to 500 per minute, as occurs with many prior devices, my improved apparatus will 105 ordinarily operate at from 2 to 15 times per minute. By roperly adjusting the contacts 20 and 21, t e off period may be made many times greater than the onperiod.

By way of illustration, we will suppose that 110 the consumers contract calls for a maximum .of 100 watts and that the contacts are set for an off period of 15 seconds. Now, if an attempt is made to connect a 500 watt heating device on the circuit it will require only about of a second to heat the thermal element 15 up to the point required for breaking the circuit. It will thus be seen that with an on period of of a second and an off period of 15 seconds, there is-no 1 possibility of maintaining the temperature of such a heating device high enough to be of service.

Referring to Fig. 2. it will be seen that instead of connecting the thermal element 15 directly in series with the load, as in Fig. 1, it is connected to the secondary winding 34 of a series transformer. This transformer has a primary winding 33, throughwhich the load current passes. The ends of the secondary winding 34 are connected by wires 11 and 12 with binding posts 3 and 6, and. the wire 11 is also connected with the line wire 1 by means of the cross connection 37. From binding post 3 extends a wire 38 to binding post 13, supporting thethermal element, a pair of switch contacts 39 being interposed in such wire and normally closed by means of the switch 30. The wire 24 which extends from one end of the solenoid 23 to binding post 5 and thence to line 2, has connected therein a pair of spaced contacts 36, adapted to be bridged by a second switch member actuated by the core 32 simultaneously with the switch member 30.

The windings 33 and 34 constitute an impedance. This is relatively low when the terminals of coil 34 are short circuited through the thermal element 15, as shown in the drawings, and relatively high when the circuit of coil 34 is open.

The operation of this arrangement is as follows: Upon the occurrence of excess load, the wire 15, receiving current from the secondary coil 34, is heated and expands until the switch finger 18 engages contact 20. This closes a circuit from line 1 through connection 37 wire 11, binding post 3, wire 38, thermal element 15, conducting link 17, switch finger 18, contact 20, wire 22, coil 23, wire 24, switch 3536, binding post 5 to line 2. This energizes solenoid 23 which pulls the core 32 to the right, thus moving switches 30 and 35 out of engagement with their respective contacts. Switch 30 opens the circuit of coil 34, thus increasing the impedance of the main line and dimming the lights 10. At the same time switch 35 opens the circuit of solenoid 23 and stops the flow of current therethrough. When the wire 15 cools sufiiciently, switch finger 18 will be drawn over against contact 21 and thus closes a circuit as follows: Beginning at one side of secondary coil 34, current flows over wires 11 and 27 to coil 26, thence through wire 25 to contact 21, spring finger 18, connecting link 17, thermal element 15, to binding post 14, thence over wires 38' and 12 back to the other side of secondary coil 34. This energizes coil 26 which restores the core and associated parts to the position shown in the drawing, thus short circuiting the terminals of coil 26 and also the terminals of coil 34, thereby reducing the impedance of the main line and permitting the lights to burn at full candle power until the thermal element acts again. It will be seen that the arrangement just described serves to cause a periodic dimming of the lights instead of extinguishing them altogether, and it will of course be understood that this particular arrangement is applicable only to an alternating current circuit.

Referring now to Fig. 3, it will be seen that this arrangement is quite similar to Fig. 1 except that, auxiliary contacts for control, ling the solenoid windings are employed. As in Fig. 1, the thermal element 15 is in series with the load through wire 1, binding post '6, wire 28, binding post 14, binding post 13, wire 38, and wire 8. \Vhen the load becomes excessive and contact finger 18 engages contact 20, the solenoid 23 is energized, as in Fig. 2, throu h a circuit including the switch 35-36. owever, in this arrangement the wire 27 extending from the coil 26 toline, as in Fig. 1, has'included therein a pair of spaced contacts 40 which are also governed by the switch 35. When, therefore, the core 32 moves to the right under the influence of coil 23, the switch 35 breaks the circuit of coil 23 at contacts 36 and establishes the circuit of coil 26 through contacts 40. Hence, when upon the cooling of the thermal element 15 the contact finger 18 engages contact 21, the coil 26 is connected directly across the line, the same as coil 23. This modification is designed for the purpose of increasing the strength of the closing solenoid, which is particularly desirable on low capacity installations.

In Figs. 4 and 5, I have shown other arrangements for dimming which are equally applicable to both direct and alternating current circuits. In these figures, the same auxiliary contacts 36 and 40, controlled by the switch 35, are employed for governing the circuits of the solenoid coils 23 and 26, and the thermal element 15 is in series with the load, as in Fig. 3.

However, in Fig. 4, instead of interrupting the main circuit when the contacts 39 are opened, as in Fig. 3, I provide means for inserting a resistance in series with the load. This resistance in Fig. 4 is shown at 41 as connected between the wires 38 and 28' in parallel with the hot wire 15. The resistance 41 is, however, normally short circuited by such hot wire, and when this short circuit is removed by the opening of switch 39,

the load current necessarily passes through resistance 41, on its way to main 8, connected with the load.

In Fig. 5, the resistance 42 is connected in shunt across the terminals of switch 39 instead of being connected like resistance 41 in the preceding figure. IVhen the switch 39 opens, therefore, the resistance 42 is thrown in series with the hot wire 15 and the load, and thus reduces the current through such wire sufficiently to allow it to cool and actuate the closin solenoid after a given period. It will be seen that by making the resistance 42 adjustable and giving it the proper value, the device may be set so that suflicient current will flow through 42 and wire 15 to maintain the latter at a temperature so high as to prevent the contact finger 18 from engaging the restoring contact 21 at all, so long as the excess load is connected to the mains. Any lights on the circuit will, of course, remain constantly dim through such a period also.

' Figs. 6, 7, S, and 9 relate to arrangements adapted for alternating circuits.

Fig. 6 is identical with Fig.1 except that the thermal element 15, instead of being connected in series with the load, is'connected by wires 46 and 49 with the secondary 46 of a series transformer. This transformer has its primary winding 44 connected directly in series with the load'through wires 28, 45, and 43. so that, asis well understood, the current in the circuit including the secondary winding 46 is always proportional to the load. The cross connection 47 between the primary and secondary circuits is provided in order to properly energize the solenoids 23 and 26, the function. of this cross connection being identical with that of cross connection 37, explained in the description of Fig. 2.

This arrangement of using a series transformer permits the adoption of a uniform thermal element of standard size for all capacities. the transformer windings being simply proportioned to suit various conditions. Moreover, the use of a transformer of this kind eliminates all danger of damage to the thermal element by short circuits.

In Fig. 7. I have shown how the thermal element can be operated by means of a secondary winding placed on the operating solenoid itself. This winding is indicated at 57 and is shown as associated with the winding 23 of the opening solenoid. Instead of the contact 20, I provide an auxiliary spring finger 52, secured to a fixed support 53, and normally in engagement with a contact 54. connected to the thermal element 15 by means of a wire 55. The secondary winding 57 has one end connected by means of a wire 58 with the opposite end of the thermal element 15, and its other end connected by means of a wire 56 with the contact 54. It will be apparent that the opening solenoid 23 is in series with the load through wires 24 and 8'. hen the ?current becomes excessive. a correspondingly increased current is generated in the secondary circuit, including the thermal element 15 and coil 57,thus permitting the element 15 to expand and the contact finger 18 to engage the finger 52 and cause it to break connection with contact 54. (the spring 19 of finger 18 being stronger than the spring of 52). The disengaging ot finger 52 and contact 54 .opens the circuit of secondary winding 57, which has heretofore served to counteract the winding 23. and permits the solenoid 23 to act and open the switch 36. The separation of contacts 52 and 54 also opens the hot wire circuit and permits the wire to cool, thus causing contact finger l8 to'engage contact 21 and energize solenoid 26. The circuit of the latter is as follows: Beginning at line 1, through wire 27, solenoid 26, wire 25, contact 21, contact finger 18, conducting link 17, thermal element 15, binding post 14, wire 55, joint 53, contact finger 52, wire 56, cross connection 59, to main 8, thence through the load back to main 9 and line 2.

Fig 8 shows my improved controlling device as applied to a three-wire alternating current circuit. The three wires are indicated at 1, 2, and 60, the line 60 running straight through to the load. The solenoid core 32 operates a switch 30 controlling line .1, as in Fig. 1, and also a switch 63 controlling contacts 62, connected with line 2. The secondary winding 46 and co-operating parts are identical in every respect with the corresponding arts shown in Fig. 6. In Fig. 8, however, this secondary wind-- ing 46 is associated with two primaries 44 and 61. The winding 44 is connected between the line 1 and main 8 by wires 45 and 43, as in Fig. 6, While the primary winding 61 is connected by wires 7 and 7 to binding posts 4 and 5 to which line 2 and main 9 are attached. In other words, the switch 6263 and the Winding 61 are interposed in the cross connection 7, which appears in Fig. 6. As a result of the arrangement shown, the current in the hot wire circuit including secondary 46, is proportional to the sum of the currents in the outside legs 1 and 2 of the three-wire circuit. No further description of this arrangement seems necessary as it operates in every respect similar to those heretofore described, the only difference being the joint control of both legs of the circuit.

It will of course, be obvious that this three-wire arrangement may be modified to produce a dimming action in the same mannor as shown in Figs. 2, 4, and 5, or the secondary winding may be associated with the actuating solenoids as in Fig. 7.

Referring finally to Fig. 9, I have illustrated the application of my controlling device to a two-phase alternating circuit. One phase is represented by the wires 1 and 64, and the other phase by the wires 2 and 65. The lines 64 and 65 run straight through to the load, while the lines 1 and 2 contain the switching devices 2930 and 6263,

. similar to those shown in Fig. 8. The solenoid coils 23 and 26 are controlled by the switch member 35, working between the two sets of contacts 36 and 40, as in Figs. 6 and 8. The hot wire 15 is connected in a permanently closed circuit. including the secondary windings 46 and 66, of two transformers, the primary windings 61 and 44 of which are connected with the lines 1 and 2, as in Fig. 8. One end of each of the secondary ,windings 46 and 66 is connected by the contact finger 18, while the opposite ends of the windings 4.6 and 66 are connected by wires 48 and 49 to binding posts 13 and 14, respectively. The current generated in secondary winding 46 flows from such winding over wire 49,-half of hot wire 15, connecting link 17, thence through contact finger 18 and common return wire 67, back to 46. The current generated iii-secondary winding 66 flows from such winding through wire48, binding post 13, the other half of hot wire 15, conduct'ng link. 17, and thence over contact finger l8 7 wire 67, back to 66. Thus, each halffof'the thermal wire 15 is heated separately by one of the transformers, but the total expansion of this wire being equal to the surnot .the expansions of its two halves,is proportional to the sum of the currents flowing in the two circuits and is therefore proportional to the sum of the currents in the two phases of the polyiphase circuit. The solenoids 23 and 26 are operatively connected in shunt. across the lines by means of the wire 2+, binding post 68, and wires 69 and 70, as will be obvious.

A similar arrangement of transformers and secondary circuits can, of course, be used in connection with a three-phase circult.

Ill. will also be understood-that the arrangement shown in Fig. 9 may be modified to produce dimming, as in Figs. :2, 4, or 5, instead of interrupting the circ'uitas deson pom

In conclusion it maybe te ou'tl that in every modification shown thekasolenoids which are controlled by the 'thennal'ele'ment take current only momentarily and therefore are not subject toheating or other troubles. It will also be noted that in every case the contact finger operated by thethermalelement is never required to while current is flowing,

It is thought/that sion the adaptabilit I of my invention wi 1 be readily fappreciated means of a common wire 67 with and common return including means circuit, said element consisting of contacts arranged to break its circuit 1 I p aml'cthc withoutfurtherdiscus; and many advantages 1. In a current-limiting device, the combination with a main circuit, of a thermal clement responsive to current flowing in said circuit, said element consisting of a hot wire fixed at its ends, a switch member to which the middle of the hot wire is mechanically and electrically connected, a. pair of contacts arranged to be engaged by said switch member. means in the main circuit including a switch for increasing the resistance oi the circuit and auxiliary circuits connected with said contacts and including each said switch member and a portion of said hot wire, one of said auxiliary circuits for opening the said main circuit switch and the other auxiliary circuit including means for closing the said main. circuit switch.

2. In a current limiting device, the combination with a main circuit, of a thermal element responsive to current flowing in said of a hot wire fixed at its ends, a switc 1 member to which the middle of said hot wire is mechanically and electrically connected, a pair be engaged by said switcl. member, a switch in the main circuit and auxiliar circuits connected with said contacts and including each said switch member and a. portion ofsaid hot wire, one of said auxiliary circuits including means for r'i ening the said. main circuit switch othcr auxiliary circuit including means .for closing the main circuit switch.

"*I'n testimony whereof I allix my signature.

- BENJAMIN E. GE'IC/IIIGLL.

in the 

